In 1890, Shibasaburo Kitazato and Emil Behring reported an experiment with extraordinary results; particularly, they demonstrated that immunity can be transferred from one animal to another by taking serum from an immune animal and injecting it into a non-immune one. This landmark experiment laid the foundation for the introduction of passive immunization into clinical practice. Today, the preparation and use of human immunoglobulin (Ig) for passive immunization is standard medical practice. In the United States alone, there is a $1,400,000,000 per annum market for human Ig, and each year more than 16 metric tons of human antibody is used for intravenous antibody therapy. Comparable levels of consumption exist in the economies of most highly industrialized countries, and the demand can be expected to grow rapidly in developing countries. Currently, human antibody for passive immunization is obtained from the pooled serum of human donors. This means that there is an inherent limitation in the amount of human antibody available for therapeutic and prophylactic usage. Already, the demand exceeds the supply and severe shortfalls in availability have been routine.
In an effort to overcome some of the problems associated with the inadequate supply of human Ig, various technologies have been developed. For example, the production of human Ig by recombinant methods in tissue culture is routine. Particularly, the recombinant expression of human Ig in CHO expression systems is well known, and is currently utilized for the production of several human immunoglobulins (Igs) and chimeric antibodies now in therapeutic use.
Mice retaining an unrearranged human immunoglobulin gene have been developed for the production of human antibodies (e.g., monoclonal antibodies) (see, for example, WO98/24893; WO96/33735; WO 97/13852; WO98/24884; WO97/07671(EP 0843961); U.S. Pat. Nos. 5,877,397; 5,874,299; 5,814,318; 5,789,650; 5,770,429; 5,661,016; 5,633,425; 5,625,126; 5,569,825; and 5,545,806).
Additionally, WO00/10383 (EP 1106061) describes modifying a human chromosome fragment and transferring the fragment into certain cells via microcell fusion.
Further, WO01/35735 describes a bovine IgM heavy chain knockout.
U.S. Pat. No. 5,849,992 issued Dec. 15, 1998 to Meade et al., as well as U.S. Pat. No. 5,827,690 issued Oct. 27, 1998 to Meade et al., describe the production of monoclonal antibodies in the milk of transgenic animals including mice, sheep, pigs, cows, and goats wherein the transgenic animals expressed human Ig genes under the control of promoters that provide for the expression of the antibodies in mammary epithelial cells. Essentially, this results in the expression of the antibodies in the milk of such animals, for example a cow.
However, notwithstanding what has been previously reported, improved methods and enhanced transgenic animals, especially cows, that produce antibodies (particularly, polyclonal antibodies) of desired species, particularly human Igs, in the bloodstream and which produce an array of different antibodies which are specific to a desired antigen would be highly desirable. Most especially, the production of human Igs in ungulates, such as cows, would be particularly beneficial given that (1) cows could produce large quantities of antibody, (2) cows could be immunized with human or other pathogens and (3) cows could be used to make human antibodies against human antigens. The availability of large quantities of polyclonal antibodies would be advantageous for treatment and prophylaxis for infectious disease, modulation of the immune system, removal of human cells, such as cancer cells, and modulation of specific human molecules. While human Ig has been expressed in mice, it is unpredictable whether human Ig will be fractionally rearranged and expressed in bovines, or other ungulates, because of differences in antibody gene structure, antibody production mechanism, and B cell function. In particular, unlike mice, cattle and sheep differ from humans in their immunophysiology (Lucier et al., J. Immunol. 161: 5438, 1998; Parng et al., J. Immunol. 157:5478, 1996; and Butler, Rev. Sci. Tech. 17:43, 2000). For example antibody gene diversification in bovines and ovines relies much more on gene conversion than gene rearrangement as in humans and mice. Also, the primary location of B cells in humans and mice is in the bone marrow, whereas in bovines and ovines B cells are located in the illeal Peyer's patch. Consequently, it would have been difficult, if not impossible, prior to the present invention, to predict whether immunoglobulin rearrangement and diversification of a human immunoglobulin loci would take place within the bovine (or other ungulate) B cell lineage. In addition, it would also have been unpredictable whether a bovine would be able to survive, i.e., elicit its normal immune functions, in the absence of its endogenous Ig or with interference from human antibodies. For example, it is not certain if bovine B cells expressing human Ig would correctly migrate to the illeal Peyer's Patch in bovines because this does not happen in humans. Also, it is not clear if human Fc receptor function; which mediates complement activation, induction of cytokine release, and antigen removal; would be normal in a bovine system.